Thinking Cap is also Party Hat

The Thinking Cap is a piece of wearable signage that lets you display what’s on your mind. The hat uses a Teensy 2.0 connected to a Bluetooth radio to allow the wearer to update the message on the fly, letting the room know what their thinking at that instant.

This hack is based off of LPD8806 controlled LED strips, which are becoming very popular for adding lots of LEDs to anything. There are five strips that need to be controlled over SPI, but the Teensy only has one SPI peripheral.

This lead to the use of multiplexer to allow for controlling each strip individually. The hat uses an interesting and low cost scheme to multiplex five channels using two 744052 dual 4 channel multiplexors and a 7400 inverter.

The Teensy can receive messages using the Bluetooth serial port protocol. The 5 x 7 pixel characters are stored in a framebuffer, and shifted around the hat to create the animation.

The result is a bright message circling around the user’s head, which can be updated with a smartphone over Bluetooth. Check out a video demo of the hat after the break.

I think I had a theory that my frame rate would be limited. A single long chain would have to wait for all the lights to be set before it could latch and update, vs setting and latching 5 smaller chains sequentially. The smaller chains would appear to refresh faster since there is less wait before latching between each one (like pipelining), though individually they would all have to wait the same amount of time between refreshes.

Though in the end, I don’t think it really matters, so yeah, it was probably for naught.

In the end it was kind of pointless to use the mux for the hat, but it’s necessary for my next piece using the LED’s which is pair of shirt and pants, with a strip running down the length of each leg and arm, as well as up the front of my abdomen/chest.

It will be annoying to have to run double lengths of cable down my legs and arms in order to chain everything, so having a scheme to mux them will help greatly.

That’s seems like about 5m of lpd8806 strip, count from 15 to 40$ (shipping included) the meter depending on “where” you get them
The board+hardware, the hat and the work…

Don’t know if the fastspi was “fixed” to run on the teensy 2.0 (it runs on the 3.0, i can confirm that) but if you can maange to make it work on it you’ll boost the framerate to “crazy speed” (for the teensy 3 that can go over 1000+ fps)

The LED strip I got was $200 shipped on ebay, it contains 52 LED’s per meter (most of the other places that were selling the strips were only 32/m), and yes it was 5m long, but I only used about 3.5m of it.